Do motion blur shutter curves work correctly?
I experimented with the shutter curve and it actually works like you expected. I have a Picture here showing tests with different shutter curves:



The white diagramm shows the curve I used for that render. As Object I took the default cube and made it glowing white on black background. I think the main trick to achive the effect that you want is to increase the shutter time to at least 1 (I used 1 for my renders) but that depends on the speeds of your objects in your scene.